The Fat Lady is the subject of a magical portrait that hangs over the entrance to the Gryffindor Tower at Hogwarts School of Witchcraft and Wizardry. Her primary role is to act as the guardian of the Gryffindor Common Room, granting access only to those who provide the correct, changing password. Though often irritable, especially when disturbed, she is fundamentally loyal to Gryffindor house and its headmaster, Albus Dumbledore. She is a constant and familiar presence in the lives of Gryffindor students throughout the series.
The Fat Lady's origins and the date her portrait was created are unknown, but she was already guarding the Gryffindor Tower long before Harry Potter's arrival at Hogwarts.
The Fat Lady is described as a “very fat woman in a pink silk dress.” She has a rather vain and proud personality, particularly regarding her singing voice, though Harry Potter notes she cannot hold a tune and her attempts at hitting high notes are powerful enough to shatter a wine glass. She takes her duties as a guardian very seriously and can be stern and short-tempered with students who forget the password or try to enter after hours. Despite her often-irritable demeanor, she is capable of great fear, as shown by her reaction to Sirius Black's attack. She is also loyal and enjoys socialising with her friend Violet, sharing gossip and drinks.
As the subject of a magical portrait, the Fat Lady possesses a range of abilities common to such enchanted objects.
Her name, “The Fat Lady,” is purely descriptive, referring to her physical appearance in the painting. Her true name, if she has one, is never revealed in the original novels.